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Indirectly prefetch board[from]

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One of the most time critical functions is move_is_check()
and in particular the call to type_of_piece_on(from) in the
switch statement.

This call lookups in board[] array and can be slow if board[from]
is not already cached. Few instructions before in the execution stream,
we check the move for legality with pl_move_is_legal().

This patch changes pl_move_is_legal() to use type_of_piece_on(from)
for checking for a king move so that board[from] is automatically
cached in L1 and ready to be used by the near follower move_is_check()

Another advantage is that the call to king_square(us) in pl_move_is_legal()
is avoided most of the times.

Speed up of this nice and tricky patch is 0.7% !

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-09-13 09:02:20 +01:00
parent f205fe1fe5
commit 3863cd191c
1 changed files with 4 additions and 4 deletions
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8
src/position.cpp
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@ -479,10 +479,9 @@ bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
Color us = side_to_move();
Square from = move_from(m);
Square ksq = king_square(us);
assert(color_of_piece_on(from) == us);
assert(piece_on(ksq) == piece_of_color_and_type(us, KING));
assert(piece_on(king_square(us)) == piece_of_color_and_type(us, KING));
// En passant captures are a tricky special case. Because they are
// rather uncommon, we do it simply by testing whether the king is attacked
@ -493,6 +492,7 @@ bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
Square to = move_to(m);
Square capsq = make_square(square_file(to), square_rank(from));
Bitboard b = occupied_squares();
Square ksq = king_square(us);
assert(to == ep_square());
assert(piece_on(from) == piece_of_color_and_type(us, PAWN));
@ -509,14 +509,14 @@ bool Position::pl_move_is_legal(Move m, Bitboard pinned) const {
// If the moving piece is a king, check whether the destination
// square is attacked by the opponent.
if (from == ksq)
if (type_of_piece_on(from) == KING)
return !(square_is_attacked(move_to(m), opposite_color(us)));
// A non-king move is legal if and only if it is not pinned or it
// is moving along the ray towards or away from the king.
return ( !pinned
|| !bit_is_set(pinned, from)
|| (direction_between_squares(from, ksq) == direction_between_squares(move_to(m), ksq)));
|| (direction_between_squares(from, king_square(us)) == direction_between_squares(move_to(m), king_square(us))));
}